Largely:
- Remove explicit `"Default is x"` since new refs show default inferred
from sig
- Inline code (useful for eventual parsing)
- Fix code block rendering (indentations)
## Description
This PR introduces a new sparse embedding provider interface to work
with the new Qdrant implementation that will follow this PR.
Additionally, an implementation of this interface is provided with
https://github.com/qdrant/fastembed.
This PR will be followed by
https://github.com/Anush008/langchain/pull/3.